Electrostatic recording head



Jan. 1, 1963 C. R. JOYCE ELECTROSTATIC RECORDING HEAD Original Filed Sept. 12, 1956 2 Sheets-Sheet l GAS AND WATE l} VAPOR JET FIXTUR E WATER VAPOR JET ADJUSTABLE I HEAD MOUNTING V INVEN TOR. CECIL R. JOYCE BY/ZM AGENT Jan. 1, 1963 c. R. JOYCE 3,071,

ELECTROSTATIC RECORDING HEAD Original Filed Sept. 12, 1956 2 Sheets-Sheet 2 INVENTOR. CECIL R4 JOYCE AGENT United States Patent The present invention relates to electrostatic recording and more particularly to a novel head construction having an array of electrodes for printing or plotting data upon a suitable responsive medium. This application is a division of pending application for patent in the name of Cecil R. Joyce, Serial No. 609,431, filed September 12, 1956, entitled Electrostatic Recording Head and Method for the Fabrication Thereof," now Patent No. 2,974,368 and assigned to the same assignee as the present application.

. In the development of electrostatic printing, effective results largely depend upon complicated circuits for character selection requiring a multiplicity of printing electrodes. In the past, and particularly where commercial production is concerned, the problem of properly arranging, separating and mounting such electrodes has introduced a prohibitive cost factor which has seriously retarde-d eiforts to meet trade demands for such equipment.

An object of the present invention is to provide a novel electrostatic recording and printing head wherein the heretofore 'high cost of such devices has been substantially reduced.

A further object of the present invention is to provide an improved electrostatic printing head in which relatively Widely deployed electrode elements are brought together into a compact closely spaced array of printing styli.

In accordance with the objects of the invention and first briefly described, there is provided a novel recording head wherein a plurality of conducting wires are arranged in spaced relation through a molded body of dielectric material with the ends of the wires exposed thus to form a linear array of electrodes, each electrode of which is' connected at its other end to a terminal connector. The head is fabricated by first securing the wires under tension, and

the terminals in a mold and then layer molding insulating material around the wires and terminals in a manner whereby the molded material is free of bubbles and internal stresses.

In the accompanying drawings:

FIG. 1 is an elevational view of a portion of apparatus employing an electrostatic head embodying one form of the present invention;

FIG. 2 is a planview of a wire holding element used in manufacturing the present invention;

FIG. 3 is a side view, partially in phantom outline, of the head of FIG. 1;

FIG. 4 is a View on an enlargedscale of a fragmentary portion of the head structure looking in the direction of the arrows on line 44 of FIG. 3;

FIG. 5 is a perspective view of one form of mold and wire tensioning mechanism for carrying out the methodof the invention;

FIG. 6 is an exploded perspective view of the head and an associated electrical connector;

FIG. 7 is' a front view of the recording head of the present invention and showing an associate-d recording medium in phantom outline; and,

vention, is shown as comprising a tapered body 10, and a flat extension 11 having a tapered end portion terminating in a narrow planar face 12 (FIG. 7), all molded of a chemically exothermic material such as epoxy resin. The opposite end panel of body 10 has embedded therein, connector units 13 and 14, each of which, as seen in FIGS. 1 and 3, includes a plurality of rows of terminals 15 extending therethrough. The inner ends of the terminals are respectively soldered to a plurality of conducting wires 16, while the outer ends thereof project as plug-in connectors engageable with the wires of a cable pulsing unit or the like, such as seen in FIGS. 1 and 6. Illustratively as seen in FIGS. 2 and 3, each connector unit is provided with three rows of terminals '15 with a wire 16 connected at one end to and leading from each terminal, and its other end terminating as a pin-shaped recording electrode 17 projecting from face 12 in a linear array, as indicated in FIG. 7.

In the present instance, connector units 13 and 14 are arranged one above the other (FIGS. 2 and 3) with all wires 16 meeting in a common row formed by passing them over a dowel 20 in spaced parallel relation with each other throughout the length of body extension 11. Thus the molded assembly includes in one portion thereof, six rows of fanned out wires 16 (FIG. 3) each row being in a transverse plane angularly spaced from each other, and all concentrated at another portion of the assembly in a single planar row. According to the present illustrated embodiment, even though eighty-two terminals are provided by connector units 13 and 14 only seventy-seven wires are used to form the linear array of exposed electrodes 17, some of which are shown in FIG. 7.

Further, for a clear understanding of the critical nature of the assembly, it is to be understood that each wire has a diameter of the order of 0.003 of an inch. Proper parallel spacing of the wires is obtained by forming accurately spaced wire seating grooves in the dowel 20, as described later during the description of the method of fabrication.

Referring to FIG. 1 illustrating a use of the head for electrostatic printing or the like, the recording head of the invention is arranged with the linear array of electrodes adjacent to a recording medium 21, in tape or sheet form, which is moved across the electrodes by means (not shown), but during which movement it is guided by suitable rollers 22 and 23 located on the opposite sides of a printing anvil 24 in such a way that the sheet 21 passes the electrode array in a direction normal to the alignment of the electrode array. Illustratively, spacing of the electrodes from medium 21 is of the order of a few thou:

FIG. 8 is an enlarged isometric view of a molding dam' sandths of an inch. For a more complete description of electrostatic printing apparatus wherein the present invention may be utilized, reference may he had to co-pending United States application, entitled Electrographic Printer, Serial No. 443,646, filed July 15, 1954, in the names of H. Epstein and F. Innes, now Patent No. 3,012,839.

A novel method for performing the steps of fabrication resulting in the complete head is set forth in detail in the earlier mentioned co-pending application Serial No. 609,431 and is described herein as one method and apparatus for producing the article herein claimed, namely the recording head. To this end there is provided an open top receptacle or mold 25, formed, as shown most clearly in FIG. 5, by removable side walls 26 preferably of metal stock, a floor 27 shaped to produce the desired molded head contour, and an end panel 28 of dielectric material, the latter being cut from a larger piece 28a of such material as will be explained presently. The floor 27 provides a horizontal surface 27a and downwardly inclined surfaces 29 and 29a at opposite sides thereof.

Dowel 20 of dielectric material, having its ends fixed in walls 26, is positioned in the mold at the junction of walls 27a and 29. Mounted on inclined wall 29a as by angle irons 30, is a platform 31 having upstanding rigid pins 32 which serve as anchoring means during tensioning of the Wires. The bottom of dowel 20 rests in a transverse arcuately shaped groovein the receptacle floor at the junction of the two surfaces 27a and 29, and is provided with 'wire spacing means comprising a row of peripheral grooves 33, FIGS. 4 and 5, each receiving one of the wires. V- grooves enable use of different wire diameters.

In order to facilitate handling and alignment of the multiplicity of fine Wires 16 in an orderly array prior to their attachment to the molding fixture, connectors 13 and 14 are inserted and secured in suitable fashion, as by gluing, in apertures 13' and 14 in a thin sheet of dielectric material 28a (FIG. 2). Individual wires 16,

are knotted at one end and thereafter soldered to one of the connector terminal pins 15, after which the opposite ends are secured in orderly array in the numbered slits 17 across the top of the dielectric sheet.

Sheet 28a is then placed in the jig as shown fragmentarily by the phantom outline 28a in FIG. 5. Thereafter individual wires are removed from the slits and secured to one of the pins 32, by means of a spring 37, after which the excess material of sheet 28a is cut away leaving panel 28.

As seen in FIG. 5, when panel 28 is in position, termijnals 15 are below dowel 20 and preferably below a plane peripheral grooves '35, equal in number to those in dowel 20 and aligned therewith to maintain uniform spacing of parallel wires. Illustratively, the axial spacing of both sets of grooves 33 and 35 may-be of the order of twenty thousandths of an inch center to center.

To tension wires 16 (only one being shown in FIG.

each is led from dowel 34, downwardly over floor 29a, platform 31 and is connected by means of a clip The final layers of material are now poured one after another until the extension 11 has the required thickness to locate the row of electrodes medially thereof. The layer pouring and particularly of the two layers of onesixteenth inch thickness immediately above and below the plane of wire prevent the formation of bubbles about the Wires, and the build-up of internal stresses as well as reducing shrinkage of the plastic molding material. Electrical arc-through in the bubbles due to gas formation therein would tend to cause carbon tracks in the plastic material shorting the wires 16 together.

When the molding operation is complete, the mold is dismantled thus to release the molded head, after which the extension is cut off transversely in close proximity to dam 38, thereby exposing the array of electrodes for final processing as exposed pointed pin members. Also as seen in FIGS. 3 and 4 dowel 20 is trimmed down to conform to the molded contour of the body of the head.

The wire ends are or may be abraded in suitable fashion as with a pig bristle brush to remove the excess plastic material adhering thereto since the plastic tends to expand beyond the tips of the exposed Wires.

It will now be apparent that a complete unitaryelectrostatic head has been devised, resulting in a head construction wherein a multiplicity of pre-stressed accurately spaced leads are so arranged as to form a single linear 1arone end connected to a selected terminal, an intermediate 36 to a coil tensioning spring 37 attached to one of the j pins 32. A selected applied tension by each of the springs 37 is of the order of one pound.

An inverted channel-shaped member 38, shown most clearly in FIG. 8, extends across the mold between walls 26 in close proximity to dowel '34. A pair of U-shaped' members 33--33 adapted to be fitted over the upstanding projections 39-39 of the member 38 thus provide a slot or aperture through which the wires,16 can be passed leaving a 4 clearance. The member 38 extends transportion passing over said dowel, and its other end terminating in an array of electrodes projecting fromthe end of said extension.

2. An electrostatic printing head according to claim 1 wherein the dowel has transverse wire receiving slots for spacing the wires one from another.

3. An electrostatic recording head, comprising a body of insulating material having a flat relatively thin extension at one end and a relatively thick portion converging into said extension, a dielectric panel molded into the outer face of said portion, a row of terminals extending through said panel below a plane through said versely of said mold and parallel to the dowel 34 at the 1 required level to permit all of the tensioned wires 16 to pass through an exposed body of grease 40, such as Dow Corning silicone grease which fills the member 38 and together with the members 33--33 forms a dam at this end of the mold to prevent the molding material from running out.

After all of the wires are attached to pins 32, the aforementioned liquid resinous material is poured into the mold cavity formed by the floor 27, and walls 26, 'such pouring being a step-by-step operation starting in the area of the inclined floor 29 thus to form a composite body of successive layers. As each layer is poured to its selected thickness, it is allowed to cool slightly be fore adding a succeeding layer. Thus, layer by layer the body grows, passing over dowel 20 to flow onto the horizontal floor surface 27a until approximately one-sixteenth of inch below the plane of the stretched wires 16. With the cooling of this layer, pouring continues until the material reaches a level approximately above the stretched wires, and then it is allowed to cool slightly. "This cooled layer is now covered with another layer of one-sixteenth thickness and also allowed to cool slightly.

extension, a dowel of dielectric material embedded-in said body at the junction of said portion and said exten sion, and a plurality of conducting wires embedded in said body, the ends of said wire being fanned out vertically and horizontally and each being connected to a selected terminal, an intermediate portion of each wire passing over said dowel, and the opposite wire ends terminating in an'array of electrodes projecting from the end of said extension.

4. An electrostatic recording head, comprising-a body of insulating material having a flatrelatively thin extension at one end and a relatively thick portion converginginto said extension, a panel molded integrally with the outer face of said portion, a row of terminals extending through said panel below a plane through said extension, a dowel of dielectric material embedded in said body at the junction of said portion and said extension, and a plurality of conducting wires embedded in said body, each having one end connected to a selected terminal, an intermediate portion passing over said dowel, and its,

other end terminating in an array of electrodes projecting from the end of said extension, the opposite ends of each wire passing over said dowel in opposite angular directions relative thereto thus to maintain said wires under tension re PQQt to their electrode and terminal ends respectively.

5. .An electrostatic recording head comprising, a body of dielectric material having a relatively thin extension terminating in a recording end and a relatively thick portion terminating in a connecting end, said portions converging together to form an intermediate relatively straight line portion, a dielectric terminal supporting member molded into the outer face of said thick portion and including a plurality of electrical connectors thereon, portions of each connector extending through said terminal supporting means into said body below a plane through said extension, a dielectric member embedded in said body at the junction of said thin extension and said thick portion and extending transversely thereacross, and a plurality of electrical connectors embedded in said body, one end of each conductor being connected to a selected connector, the intermediate portion of each conductor passing over said dielectric member with a portion of each conductor on one side of said dielectric member being being angled away from the portion of the conductor on the opposite side of said dielectric memher, the other end of each conductor terminating in an electrode forming a recording stylus at said recording head.

6. An electrostatic recording head comprising, a

plurality of rows of tensioned lead wires terminating at one end in an array of electrodes arraged in parallel spaced apart relation one with another, terminals attached respectively to the other ends of said wires, a dielectric dowel for converting said rows of wires into a common plane, and an insulating material molded around and about said wires and said dowel thereby embedding the same therein.

7. An electrostatic recording head comprising, a plurality of rows of tensioned lead wires terminating at one end in an array of electrodes arranged in parallel spaced apart relation one with another, terminals attached respectively to the other ends of said wires, a dielectric dowel for converting said rows of wires into a common plane, said dowel being provided with a plurality of transverse slots efiectively spacing said wires in said common plane one from another, and an insulating material molded around and about said wires and said dowel thereby embedding the same therein.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN ELECTROSTATIC RECORDING HEAD, COMPRISING A BODY OF INSULATING MATERIAL HAVING A FLAT RELATIVELY THIN EXTENSION AT ONE END AND A RELATIVELY THICK PORTION CONVERGING INTO SAID EXTENSION, A PANEL MOLDED INTO THE OUTER FACE OF SAID PORTION, A ROW OF TERMINALS EXTENDING THROUGH SAID PANEL BELOW A PLANE THROUGH SAID EXTENSION, A DOWEL OF DIELECTRIC MATERIAL EMBEDDED IN SAID BODY AT THE JUNCTION OF SAID PORTION AND SAID EXTENSION, AND A PLURALITY OF CONDUCTING WIRES EMBEDDED IN SAID BODY, EACH HAVING ONE END CONNECTED TO A SELECTED TERMINAL, AN INTERMEDIATE PORTION PASSING OVER SAID DOWEL, AND ITS OTHER END TERMINATING IN AN ARRAY OF ELECTRODES PROJECTING FROM THE END OF SAID EXTENSION. 